The present invention relates generally to access doors and more particularly to access doors for aerospace vehicles that are opened by an external umbilical for purposes such as pre-launch environmental control.
Aerospace launch vehicles such as rockets comprise a plurality of access doors and covers through their outer moldline surfaces for access to internal structure and subsystems. One type of access door of the known art provides internal access to a launch vehicle, which may include an internal manifold and ducting, for pre-launch environmental control such as air conditioning. In operation, an external detachable umbilical forces the access door open and induces a flow of air from the umbilical into the launch vehicle through the internal manifolds and ducting. When the air flow must be discontinued, the umbilical is removed from the launch vehicle and the access door automatically closes.
The access door must be capable of closing automatically because the umbilical is removed during lift-off of the launch vehicle. Accordingly, the access doors must be opened by an external umbilical and must further be self-closing or closed by a remote device. Moreover, the access doors must be capable of remaining closed during launch, thereby withstanding the dynamic, thermal, and pressure environments induced during flight.
One self-closing access door of the known art uses a pan-shaped plug that is circumferentially spring-loaded with extension springs to hold the door closed. Generally, the springs are mounted to the rear of the plug and to the internal moldline of the vehicle structure. When the door is forced open by an external source, the rear of the plug moves which extends the springs. When the external source is removed, the springs force the door closed against the vehicle structure. However, there is no additional mechanism to automatically secure the door to the vehicle structure after the external source is removed.
In one form, the access door comprises twenty (20) extension springs positioned around the circumference of the plug, along with a plurality of additional structure and fasteners to support operation of the access door. As a result, the access door is relatively complicated and requires a substantial amount of resources for fabrication and assembly, especially at the vehicle level. The completed access door assembly in one known form weighs approximately 15 pounds, which is relatively heavy for an aerospace application.
In operation, the extension springs are designed to maintain a minimum load, i.e. prevent the door from opening under a certain load, while the door is closed. A load approximately four times the minimum load is required to fully open the door due to the number of extension springs employed. Accordingly, if a launch vehicle increases in size and must be designed for more extreme environments during flight, the access door of the known art will only further increase in complexity and cost.
Other known art access doors employ externally mounted spring-loaded hinges, wherein the external umbilical system lifts the door up and swings the door into an open position to induce the air flow. When the air flow is to be discontinued, the umbilical releases the door and the spring-loaded hinge forces the door closed against the outer moldline surface of the vehicle. Unfortunately, since the access door must swing out and into the path of the umbilical, the access door may interfere with the umbilical and cause problems with release of the umbilical during lift-off. As a result, both the umbilical system and the launch vehicle may be damaged, which could possibly threaten the safety of flight operations.
Additional known art access doors comprise a sliding guillotine door, wherein the umbilical system slides the door up and open to induce the fluid flow. However, the design of the sliding guillotine door is relatively complex in order to withstand the flight environment after launch, and the probability of the sliding door binding during flight operations is relatively high. As a result, the sliding guillotine door is undesirable for a variety of launch vehicles and environments.
Known art access doors, therefore, are relatively complex and may be incapable of withstanding certain launch environments. As a result, access doors have been structurally complex, which results in heavier and more expensive launch vehicles. Furthermore, access doors of the known art increase the probability of failure of the umbilical system and/or the access door during launch operations when the umbilical fails to release from the launch vehicle.
Accordingly, there remains a need in the art for a reliable self-closing access door that comprises a relatively simple structure in order to reduce weight and further to simplify fabrication and assembly for reduced costs.
In one preferred form, the present invention provides a self-closing access door that comprises two (2) door panels secured to a spring-loaded hinge that is further secured to surrounding structure. The spring-loaded hinge holds the door closed against the surrounding structure, and when an external source such as a umbilical engages one or both of the panels, the panels are forced open against the forces applied by the spring-loaded hinge. When the external source is removed from the door panels, the spring-loaded hinge forces the door panels closed against the surrounding structure.
The self-closing access door further comprises a plurality of latches that are attached to the door panels to firmly secure the door panels to the surrounding structure. The latches are preferably attached to the door panels using latch supports, which are generally L-shaped brackets attached to the interior of the door panels. The latches further comprise latch hooks, which specifically engage the surrounding structure to secure the door panels in the closed position.
In another preferred form, the self-closing access door of the present invention comprises a cover plate that is attached to the surrounding structure. The spring-loaded hinge is secured to the cover plate rather than directly to the surrounding structure, and the latches engage the cover plate to firmly secure the door panels in the closed position. Generally, the cover plate is circular in shape and defines a hollow center portion. The cover plate further comprises a lateral support that extends across the hollow center portion, an inner lip, and an outer lip. The spring-loaded hinge is secured along the lateral support and thus extends across the hollow center portion of the cover plate. The outer lip is attached to the surrounding structure, and the latches engage the inner lip to secure the door panels in the closed position.
To limit the overall distance that the door panels are opened, the spring-loaded hinge further comprises a door stop. The door stop generally defines a xe2x80x9cCxe2x80x9d configuration, thereby having a flange on each side. Additionally, the door stop is separately attached to the spring-loaded hinge in the preferred embodiment of the present invention. The door panels are preferably secured to the spring-loaded hinge using rivets, and the spring-loaded hinge further comprises a tab portion on each side of the spring-loaded hinge adjacent the door stop. Accordingly, when the door panels are opened a certain predetermined distance, the tab portions along the spring-loaded hinge engage the flanges of the door stop to prevent further movement of the door panels. The door stop is also preferably riveted to the spring-loaded hinge, although other attachment methods known in the art such as adhesive bonding may also be employed.
When the self-closing access door is assembled to the launch vehicle, the hinge-line of the spring-loaded hinge is aligned with the direction of flight of the launch vehicle. The hinge-line is aligned with the direction of flight, and also the direction of the air stream, so that the probability of aerodynamic forces opening the door panels during flight is minimized.
In operation, the latches are manually or automatically disengaged, and an external umbilical engages the outer surface of the door panels to apply an inward force to open the access door until the tab portions of the spring-loaded hinge engage the flanges of the door stop. Once the door panels are open, the umbilical system induces fluid flow, e.g. air conditioning, into a manifold and additional ducting within the launch vehicle. When the fluid flow must be discontinued, the umbilical is removed from the door panels and the spring-loaded hinge forces the door panels closed against the inner lip of the cover plate. The latch hooks then engage the inner lip of the cover plate to firmly secure the door panels to the cover plate so that the door panels do not open during flight operations.
As a result, a relatively simple and reliable self-closing access door is provided that has a minimal number of parts and is relatively light weight. The self-closing access door is furthermore simple to fabricate and assemble to the launch vehicle, thereby providing both weight and cost savings over access doors of the known art.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.